/*
 * LensKit, an open-source toolkit for recommender systems.
 * Copyright 2014-2017 LensKit contributors (see CONTRIBUTORS.md)
 * Copyright 2010-2014 Regents of the University of Minnesota
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
package org.lenskit.util.io;

import javax.annotation.Nonnull;
import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * Simple implementation of an Iterator that wraps a object stream's data. This is
 * suitable for use implementing {@link ObjectStream#iterator()}.
 *
 * @param <T> The type of value in the iterator.
 */
public class ObjectStreamIterator<T> implements Iterator<T> {
    private ObjectStream<T> stream;
    private boolean hasNextCalled;
    private T next;

    /**
     * Construct a new iterator from a stream.
     *
     * @param stream The stream to wrap.
     */
    public ObjectStreamIterator(ObjectStream<T> stream) {
        this.stream = stream;
    }

    @Override
    public boolean hasNext() {
        if (!hasNextCalled) {
            next = stream.readObject();
            hasNextCalled = true;
        }

        return next != null;
    }

    @Nonnull
    @Override
    public T next() {
        if (!hasNextCalled) {
            next = stream.readObject();
        }
        if (next == null) {
            throw new NoSuchElementException();
        }

        final T n = next;
        next = null;
        hasNextCalled = false;
        return n;
    }

    @Override
    public void remove() {
        throw new UnsupportedOperationException();
    }
}
